Curable resin compositions including an epoxy resin and a phenolic hydroxy group-containing resin are used in an adhesive, a molding material, a paint, a photoresist material, a color developing material, and the like, and in addition, widely used in the electric and electronic field as a semiconductor encapsulating material, an insulating material for printed wiring board, and the like due to the fact that a cured product obtained therefrom is excellent in properties such as heat resistance and moisture resistance.
In the field of printed wiring board among the various applications, with a movement toward smaller size and higher performance of electronic devices, a tendency to increase the density of semiconductor devices by narrowing wiring pitch is remarkable, and as a semiconductor mounting method in response to the situation, a flip-chip connection method in which a semiconductor device and a substrate are bonded via a solder ball is widely used. The flip-chip connection method is a semiconductor mounting method according to a so-called reflow method in which a solder ball is placed between a wiring board and a semiconductor and then all the components are heated to melt-bond the components, and therefore the wiring board is exposed to a highly-heated environment during reflowing the solder. For this reason, when the wiring board thermally shrinks in the highly-heated environment, a large stress may occur on the solder ball which connects the wiring board and the semiconductor to cause connection failure of wirings. Accordingly, a material having a, low thermal expansion coefficient is demanded for an insulating material to be used in a printed wiring board.
In the field of semiconductor encapsulating material, the temperature in the reflow processing has been increased due to a shift to lead-free solder, and improvement in solder clack resistance (reflowability) is demanded. Thus, as a semiconductor encapsulating material, a material exhibiting high heat resistance and low moisture absorption rate in terms of its cured product is demanded.
In addition, in recent years, a lead-free solder having a high melting point has become a main stream owing to legal regulation for environmental issues and the like, and therefore, a temperature for reflow has been increased. Under the situation, connection failure due to warpage of a printed wiring board caused by a change in volume of an insulating material during reflow has become a serious problem. Accordingly, a material which shows a small change in volume after thermal history is demanded.
In order to meet the demands, for example, PTL 1 describes that a thermosetting resin composition containing as a main agent a naphthol novolac type epoxy resin which is obtained by reacting naphthol, formaldehyde, and epichlorohydrin solves technical objects such as low thermal expansion.
However, the naphthol novolac type epoxy resin is recognized to exhibit some improvements of a cured product obtained therefrom in heat resistance, thermal expansion coefficient, and moisture absorption rate as compared with a general phenol novolac type epoxy resin, and however, the levels of the high heat resistance, low thermal expansion, and low moisture absorption rate, which have been demanded in recent years, have not been sufficiently satisfied. Furthermore, a cured product obtained from the resin is liable to cause the connection failure of a printed wiring board as mentioned above due to a large change in volume through thermal history.